Content-based networks are described in A. Carzaniga, M. J. Rutherford, A. L. Wolf. A routing scheme for content-based networking. Department of Computer Science, University of Colorado, June 2003, the contents of which are herein incorporated by reference.
In content routed networks, one of the factors that determine network scalability is the limited number of TCP connections supported by each router. Between any two adjacent content routers, both control and customer data needs to be exchanged. Within the control data flows, two distinct protocols are defined; the XML Link State Protocol (XLSP) and XML Subscription Management Protocol (XSMP), both of which are components of the Implicit Routing Protocol (IRP). Refer to co-filed application Ser. No. 60/530,615, which is herein incorporated by reference. In this example, there are three application protocol streams being exchanged between each pair of content routers: an XSMP control stream, an XLSP control stream, and a data stream.
A traditional method for passing these three data flows between devices would be to establish separate TCP connections for each data flow. Multiplexing and de-multiplexing of the data at each end would be accomplished via distinct TCP port numbers. However, this technique has two significant drawbacks:                1. The number of TCP connections supported by any one networking device may be (relatively) small, and hence the wasteful usage of TCP connections would quickly limit the size and scalability of the network.        2. In a firewalled environment, the administrative overhead of configuring the firewalls to allow each type of connection significantly increases the administrative effort required to deploy the content routed network.        
As an example, in FIG. 1, consider the relatively small network 1. Here, the topology includes seven content routers 2, interconnected with thirteen XML links 3. Using TCP multiplexing, a total of thirty nine connections would be required. Each XML link 2 between a pair of content routers requires three TCP connections under this scheme since one TCP connection is needed to exchange customer data, which in a content-routed network is the events or documents that are being routed, a second TCP connection is needed for the XLSP protocol, and a third TCP connection is needed for the XSMP protocol. It is apparent that TCP connections would quickly limit network scalability, as the number of routers increases into the hundreds and number of XML links increases into the thousands or tens of thousands. Moreover, as new inter-router protocols are developed to enable new services or capabilities within the content routed network 1, yet more TCP connections would be required between a pair of routers connected with an XML link, further compounding the problem.